It is well known that nitrate in tomato fruits causes heavy detinning in canned tomato juice. It is desirable that nitrate nitrogen (NO
3-N) concentration in the fruit be below 3ppm for canning.
To investigate the effects of plant growth regulators on the accumulation of NO
3-N, and the yield and appearance of tomato fruit, a series of, studies were conducted in the winter of 1968 and in the summers of 1969 and 1970. Fourteen tomato cultivars were compared as to the fruit NO
3-N concentration in the 1969 season.
Gibberellin (GA
3) 25 and 50ppm, whether applied to the flowers, the clusters, or a whole tomato plant reduced NO
3-N concentration in the fruit, as well as fruit size and yields. Delayed maturation was also observed.
When the tomato flowers and clusters were treated with the auxins, PCPA (p-chlorophenoxy acetic acid) 15ppm, TR (4-chloro-2-hydroxy methyl phenoxy acetic acid) 100 and 200ppm and RP (4-chloro-2-folmyl phenoxy acetic acid) 100 and 200 ppm, increased NO
3-N concentration in the fruit was observed. Fruit size and yields were also increased. The time of maturation was accelerated by the auxin treatments. Among auxins, PCPA and TR were found to be highly effective on these points, while RP was less so.
By treating clusters with GA
3 and auxin together, it was found that the effect on fruit growth, yield and maturation time was approximately in between that caused by single treatments of GA
3 or auxin alone. Fruit NO
3-N concentration differed depending whether or not PCPA, RP, or TR had been combined with GA
3 in the treatment. The heaviest yield of fruit, containing NO
3-N below 3ppm resulted from a combined treatment of GA
3 25ppm with PCPA 7.5ppm on the clusters.
The effects of these plant growth regulators on a whole plant varied with their concentrations and spraying times. A single treatment of GA
3 25ppm, and the treatment of GA
3+RP decreased both the yield and NO
3-N content in the fruit. The single treatment of RP 200ppm increased the yield and NO
3-N content in the fruit but showed no significant effect of spraying times.
Chico was found to be more sensitive to the plant growth regulators than Heinz 1370.
The highest concentration of NO
3-N in the fruit was found in Fireball and Coldset, followed by Epoch, Chico, Kurikoma and Taiho, Heinz 1409, ES-24, VF-36 and other late maturing cultivars of the large fruit type were of very low nitrate content. Heinz 1409 was judged to be the most suitable cultivar based on the yield and low nitrate concentration in the fruit.
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